Atkins Diet Can Raise Heart Risks

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But how does the cardiovascular system fare on a high-fat regimen when weight remains stable? "Weight loss confounds the results, and we wanted to compare these diets without that possible confounder," Miller explained.

For this trial, 18 healthy adults completed four weeks each on the Atkins (50 percent fat), South Beach (30 percent fat) and Ornish (10 percent fat) diets.

People on the Atkins diet had increased levels of LDL ("bad") cholesterol, more constricted blood vessels and an increase in blood markers for inflammation, some by as much as 30 percent or 40 percent, the researchers said.

The results were less clear for the Ornish or South Beach regimens. In those diets, markers for inflammation remained stable or dipped by up to 20 percent, the researchers found.

Another study followed up on reports from the 1970s that Mormons experience fewer deaths from heart disease.

Previous researchers had assumed that a prohibition on tobacco use among Mormons was the reason, but the current researchers hypothesized that there were additional factors at play.

Indeed, people who reported fasting regularly had a lower risk of developing coronary artery disease. The study adjusted for various factors including resting on the Sabbath, avoiding tea and tobacco, and age and body mass index.

The study did not put a time limit on fasting, but the religious teachings of Mormons do include fasting once a month for about 24 hours.

It could be that self-proclaimed fasters have better control of their diet in general, or fasting may prompt some kind of protective biological mechanism, said Benjamin Horne, senior author of the study, director of cardiovascular and genetic epidemiology at Intermountain Medical Center and adjunct assistant professor of biomedical informatics at the University of Utah in Salt Lake City.

Still, the study has raised more questions than it has answered, including whether to fast at all and for how long, he said. Horne warned that diabetics, in particular, should not start fasting until more is known.